Sensing torque and/or thrust in a shaft, particularly in larger drive shafts, for example, in marine drives, wherein the drive shaft is also subjected to a significant amount of thrust, generally results in the torque reading being colored by the degree of thrusts applied to the shaft or vice versa. In this and other applications it is sometimes desirable to obtain an accurate reading of torque independent of thrust, but there are few if any sensor systems capable of so selecting.
It is known to detect torque by sensing the pressure between gear teeth for example, i.e. sensing the pressure or compression between the teeth, however, this is not particularly satisfactory.
It is also known to provide torque sensing elements in a coupling to measure the pressure through the drive connection to define the torque see U.S. Pat. No. 3,813,933 issued Jun. 4, 1974 to Weiss et al.; and U.S. Pat. No. 4,723,450 issued Feb. 9, 1988 and U.S. Pat. No. 4,754,652 issued Jul. 5, 1988 both to Coulter.
U.S. Pat. No. 4,765,191 issued Aug. 23, 1988 to Kume describes a system wherein the tightening of a threaded connection through which thrust is transmitted axially displaces an element and by monitoring the axial displacement the transmitted torque is assessed or measured.
U.S. Pat. No. 3,956,930 issued May 18, 1976 describes a drive system wherein a universal joint type structure wherein the cross elements are replaced with a integral ring shaped body through which the torque is transmitted and which functions as a force transducer. The integral struts are provided with strain sensors that senses the strain in the struts to provide an indication of the torque being transmitted.